This invention relates to a process for the manufacture of aliphatic phosphonic acids, and more particularly to a process for the manufacture of a 2-haloethylphosphonic acid and still more particularly, to the manufacture of 2-chloroethylphosphonic acid.
It is known in the art, that certain aliphatic phosphonic acids, particularly 2-haloethylphosphonic acids and derivatives thereof, are valuable as plant growth regulators in the agricultural field. The chloro compound, i.e. 2-chloroethylphosphonic acid has been used extensively as a plant growth regulator for increasing crop yield of, for example, pineapples, soybeans, and the like. The usefulness of these compounds is illustrated for example in the publication of Nature, vol. 218, page 974 (1969) by Cooke and Randall; and U.S. Pat. No. b 3,879,188, issued Apr. 22, 1975, entitled "Growth Regulation Process" invented by Fritz, Evans, and Cooke and assigned to the assignee of this application.
Processes for the manufacture of aliphatic phosphonic acids, more particularly, 2-chloroethylphosphonic acid have been described, for example in
A. U.S. Pat. No. 3,787,486; PA1 B. U.S. Pat. No. 3,808,265; PA1 C. U.S. Pat. No. 3,888,953; PA1 D. British Pat. No. 1,187,002; PA1 E. British Pat. No. 1,229,593; PA1 F. British Pat. No. 1,356,688; PA1 G. British Pat. No. 1,373,513; PA1 H. in certain relevant articles by Kabachnik, particularly Gefter and Kabachnik, Plasticeskie Massy, 1961, No. 1, pages 63-64; and PA1 I. Chem. Abstracts, 1962, vol. 56, col. 501(g). PA1 a. reacting the diester and the anhydrous hydrogen halide at a first temperature of at least 100.degree. C, at a low pressure and for a first period of time to form a first reaction product; PA1 b. subsequently reacting the first reaction product and the anhydrous hydrogen halide at a second temperature of at least 100.degree. C, at a high pressure, said high pressure higher than said low pressure, for a second period of time to form a second reaction product; and PA1 c. removing the aliphatic halides from at least one reaction product. PA1 1. vinyl phosphonic acid, PA1 2. 1-chloroethylphosphonic acid, PA1 3. 2-chloroethylphosphonic acid, PA1 4. 1-chloropropylphosphonic acid, PA1 5. 2-chloropropylphosphonic acid, PA1 6. 2-chlorobutylphosphonic acid, PA1 7. methylphosphonic acid, PA1 8. ethylphosphonic acid, PA1 9. propylphosphonic acid, and PA1 10. butylphosphonic acid. PA1 i. introducing continuously into the first and second reaction products an entrance stream comprised of anhydrous hydrogen chloride;
All of the foregoing references are incorporated herein by reference.
Generally, the following three-step process is described in these references: ##STR1##
Generally, one of the most critical steps in the process is PROCESS STEP III, the cleavage of the diester (d) with hydrogen chloride.
PROCESS STEP I, can, for example, be carried out as described in U.S. Pat. No. 3,888,953. This patent describes a process for the manufacture of tris(2-chloroethyl)phosphite (c) by simultaneously adding ethylene oxide (b) and phosphorus trichloride (a), in a molar ratio of between about 3.2:1 and about 3.9:1, to preformed tris(2-chloroethyl)phosphite (c) at a temperature between 0.degree. C and about 10.degree. C.
PROCESS STEP II, can for example, be carried out as described in British Pat. No. 1,229,593. This patent describes a process which involves heating to a temperature of between 140.degree. C and 160.degree. C a tris(2-chloroethyl) phosphite (c) in the presence of an organic solvent inert to the reaction to produce a bis(2-chloroethyl)2-chloroethylphosphonate (d).
As indicated previously, the critical step in the manufacture of aliphatic phosphonic acids, and more particularly 2-chloroethylphosphonic acid, is PROCESS STEP III, the cleavage of the diester (d) with a hydrogen halide.
One process for the manufacture of 2-haloethylphosphonic acid and derivatives thereof, is the cleavage of the corresponding diester with aqueous HCl. The aqueous HCl acid cleavage is a process well known in the art, and is illustrated, for example, in the text book of Kosolapoff, entitled "Organophosphorus Compounds", John Wiley & Sons, Inc., New York, around 1950, page 139. This reference indicates that esters of phosphonic acids are cleaved by hot hydrochloric and hydrobromic acid at atmospheric pressure.
U.S. Pat. No. 3,787,486 also describes a process for the manufacture of 2-chloroethylphosphonic acid which comprises treating bis(2-chloroethyl)-2-chloroethylphosphonate (d) under autogenous pressure and a temperature of about 100.degree. C to 145.degree. C with aqueous hydrochloric acid of about 20% to 45% strength to produce 2-chloroethylphosphonic acid. It is therefore well known in the art to use aqueous hydrochloric acid for cleaving the diester and to use aqueous hydrochloric acid under pressure.
Another process for the manufacture of 2-haloethylphosphonic acid and derivatives thereof, is the cleavage of the diester with anhydrous HCl at 100.degree. C to 160.degree. C. Anhydrous HCl acid cleavage is also well known in the art, as described, for example, by Gefter and Kabachnik, Plasticeskie, Massy, 1961, No. 1, pages 63-64.
British Pat. No. 1,187,002 describes a process for producing 2-haloethylphosphonic acid by introducing anhydrous HCl or HBR from an outside source into the diester which is stable at a temperature of above 140.degree. C and heating the reaction mixture to a temperature of 140.degree. C to 165.degree. C for a period of time.
British Pat. No. 1,356,688 describes the manufacture of 2-chloroethylphosphonic acid by cleaving the diester with gaseous hydrogen chloride, with the exclusion of water, under elevated pressure at a temperature in the range of 100.degree. C to 200.degree. C.
Thus, the manufacture of 2-haloethylphosphonic acid by the cleavage of the corresponding diester with anhydrous HCl at atmospheric pressure and at elevated pressures is well known in the art.
Variations on the above processes for the manufacture of 2-haloethylphosphonic acid by cleavage of the diester are also well known in the art.
For example, British Pat. No. 1,373,513 describes a process for the manufacture of 2-chloroethylphosphonic acid which comprises cleaving the diester (d) with aqueous hydrochloric acid, optionally in the presence of gaseous hyrogen chloride, at a temperature of about 100.degree. C and under an elevated pressure, continuously or discontinuously distilling off the 1,2-dichloroethane formed during the reaction and maintaining an elevated pressure by adding gaseous hydrogen chloride continuously or discontinuously during the reaction.
Another variation on the process of cleaving the diester is described in U.S. Pat. No. 3,808,265 which describes a process for the manufacture of 2-chloroethylphosphonic acid by reacting the diester (d) and concentrated aqueous hydrochloric acid under pressure of injected hydrogen chloride gas sufficient to replenish the reacted HCl and maintain the concentration of the aqueous hydrochloric acid above about 23% at a temperature of about 100.degree. C to 145.degree. C, cooling the reaction product to obtain a two phase liquid system consisting of an aqueous phase containing 2-chloroethylphosphonic acid and an organic phase containing ethylene dichloride, drawing off the ethylene dichloride phase and recovering 2-chloroethylphosphonic acid from the aqueous phase.
All of the above processes related to PROCESS STEP II involve the acid cleavage of the ester groups from the diester of the phosphonic acid to yield the corresponding phosphonic acid. ##STR2##
This cleavage reaction for the manufacture of phosphonic acid occurs in a stepwise manner. The diester is converted to the half ester which, in turn, is cleaved to the phosphonic acid. ##STR3##
This reaction is an example of a consecutive reaction.
For example, cleavage of the bis(2-chloroethyl)-2-chloroethyl phosphonate (the diester), by known prior art methods utilizing anhydrous HCl, depending upon reaction conditions and concentrations can produce from 45 to 84% 2-chloroethylphosphonic acid and from 3 to 30% of the mono-2-chloroethyl-2-chloroethyl phosphonate (the half ester).
A major impurity in the manufacture of 2-haloethylphosphonic acid, is the half ester of the corresponding acid.
It is highly desirable when applying 2-haloethylphosphonic acid, to plants, that the compositions applied be sufficiently free of impurities such as half esters of 2-haloethylphosphonic acids, to avoid the toxic, or potentially toxic effects of these impurities on plants. It is, thus, highly desirable to either remove the half ester from the crude reaction mixture obtained from the cleavage of the diester of the corresponding acid or to obtain, within reasonable operating parameters i.e. time, pressures, concentrations, etc. substantially complete reaction of the diester and half ester to 2-chloroethylphosphonic acid.
Generally, attempts have been made to purify 2-haloethylphosphonic acid manufactured from the prior art processes.
U.S. Pat. No. 3,626,037 describes the extraction with benzene of the mono ester of 2-chloroethylphosphonic acid from a reaction mixture containing the mono ester and 2-chloroethylphosphonic acid. The disadvantages of using benzene as a commercially practical extracting solvent are that it is highly flammable, acutely toxic to humans and gives poor phase separation when used as an extracting solvent for the half ester of haloethylphosphonic acid.
British Pat. No. 1,187,002 describes the extraction of the mono ester of 2-haloethylphosphonic acid from the crude reaction mixture with a halo-hydrocarbon of from 1 to 8 carbon atoms, such as chlorobenzene, dichlorobenzene, chloroform, tetrachloroethylene and preferably methylene chloride or ethylene dichloride. The disadvantages of using halo-hydrocarbons as commercially practical extracting solvents are that they are highly toxic to humans and a poor extracting solvent for the purification of 2-haloethylphosphonic acid.
The assignee attempted to solve the problem of manufacturing pure 2-haloethylphosphonic acid by extracting the half ester from an aqueous crude reaction mixture of the aliphatic phosphonic acid and the half ester by using an alkyl ester of carbonic acid, preferably diethylcarbonate, as an extracting solvent. The alkyl ester of carbonic acid may be recovered for re-use in the process. This process is described in U.S. Pat. No. 3,896,163.
A further attempt by the assignee to solve the problem of manufacturing pure 2-haloethylphosphonic acid, resulted in a process for separating an aliphatic phosphonic acid from an aliphatic phosphonic acid half ester, by extracting the half ester from an aqueous mixture, containing sodium sulfate, the aliphatic phosphonic acid and the half ester by using a halo-substituted alkyl of from 1 to 8 carbon atoms as an extracting solvent.
One serious drawback with attempting to obtain the highly pure aliphatic phosphonic acids necessary for commercial use by the addition of an extracting process to the process of manufacturing is that this extracting process involves an additional step with its concomitant increase in cost both in capital and operating expenses.
An object of this invention is to provide a novel process for manufacturing aliphatic phosphonic acids.
Another object of this invention is to provide a process for manufacturing highly pure aliphatic phosphonic acids at a low cost.
Still another object of this invention is to provide a novel manufacturing process which is particularly suitable for manufacturing 2-haloethylphosphonic acids, and more particularly 2-chloroethylphosphonic acid.
Still another object of this invention is to provide a novel process which is particularly suitable for manufacturing 2-haloethylphosphonic acids of highly pure nature under economically reasonable process parameters.
These and other objects of this invention will be more apparent from reading the following detailed description thereof.